Technical Abstract:
Bilateral ovulation may be a heritable trait that could improve prolificacy and fertility in ruminants, because bilateral double ovulations were reported to increase early embryonic survival compared to unilateral double ovulations. The current study tested the hypothesis that early embryonic survival is increased in bilateral ovulations due to enhanced luteal function. Cows selected for multiple ovulations (n = 91) were examined by ultrasound at insemination to determine the number and diameter of all follicles >/= 8 mm, at the mid-luteal phase to determine CL location, and at 60 days post-insemination to determine fetal location. Ewes (n = 26) were bred to a fertile ram and reproductive tracts were collected at slaughter on days 12 to 19 after breeding. CL were weighed and frozen in liquid nitrogen for determination of mRNA expression of steroidogenic enzymes. In cows, unilateral right twins had the greatest number of follicles >/= 8 mm on the right ovary (2.4 +/ 0.1 vs. 0.7 +/ 0.1) and unilateral left twins had the greatest number of follicles >/= 8 mm on the left ovary (2.5 +/ 0.1 vs. 0.8 +/ 0.2) with bilateral twins intermediate in numbers of follicles for each ovary (1.8 +/ 0.1 right vs. 1.5 +/ 0.1 left; P < 0.0001). Bilateral double ovulation (n = 36) did not significantly increase pregnancy rate compared to unilateral double ovulations (61.1 vs. 50.9, P = 0.3), and there was no difference in follicle diameter or progesterone concentration and CL diameter during the luteal phase between unilateral and bilateral double ovulations. In ewes, there were no differences in pregnancy rate, CL weight, serum progesterone concentrations, or steroidogenic enzyme mRNA expression between bilateral and unilateral double ovulations. Bilateral double ovulations did not enhance pregnancy rates or luteal function as compared to unilateral double ovulations. From these data, we conclude that the number of follicle >/= 8 mm on each ovary at insemination may be an indicator of ovulatory phenotype.